1. Human Genetics

2. Humans have 23 pairs of chromosomes, containing 3 billion letters of DNA code and 24,000 genes.
One set comes from MOM and one set comes from DAD. There are 22 pairs of autosomes and 1 pair of sex chromosomes, X and Y.
XX = female
XY = male

3. Probability of having a girl or boy
Mom
X X X Y XX
Girl XY
Boy
Dad

4. Human Genetics Patterns of inheritance: Autosomal Dominant
We receive one of each
chromosome from mom and
one from dad.
Geneticists study how genes are
inherited in offspring.
Autosomal Dominant
Autosomal Recessive
Sex-linked

5. What is a Pedigree?
A pedigree is a chart of the genetic history of family over several generations.
Scientists or a genetic counselor would find out about your family history and make this chart to analyze.
A pedigree is a chart of the genetic history of family over several generations. Scientists or a genetic counselor would find out about your family history and make this chart to analyze it. For example, a couple might like to know their chances of having a child that has muscular dystrophy. So the scientists or a genetic counselor would find out who had muscular dystrophy in the mother’s and/or father’s families. This information would be used to and then calculate the probability of the couple having a child with MD.

6. Constructing a Pedigree
Female
Male
You must learn the symbols of the pedigree charts before you can start to learn how to interpret it. These are the symbols that represent a male and a female.

7. Connecting Pedigree Symbols
Examples of connected symbols:
Married Couple
Siblings
These symbols also represent relationships between people. some may have to each other.

8. Example What does a pedigree chart look like?
This is just an example of a pedigree and there can be many more different types.

9. Symbols in a Pedigree Chart
Affected
Autosomal carrier
Deceased
These are examples of different types of symbols. These symbols would be the same for males or for females, except for X-linked carrier which is only used for females. So an affected male would be a square that is filled in completely. A deceased female would be a circle with a diagonal slash.

10. Interpreting a Pedigree Chart
Determine if the pedigree chart shows an autosomal or X-linked disease.
If most of the males in the pedigree are affected the disorder is X-linked
If it is a 50/50 ratio between men and women the disorder is autosomal.
When interpreting a pedigree chart of a family with a disease like muscular dystrophy, it is important to consider two steps. The first is to determine if the disorder is autosomal or X-linked.
If the disorder is X-linked most of the males will have the disorder because the Y-chromosome cannot mask the affects of an affected X-chromosome. A female can have the disorder, but it would be a very low percentage. For a female to be affected, she would have had to receive an affected gene from the mother and the father. This means that the father would have the disorder and the mother was a carrier.
In an autosomal disorder, the disorder is not found on the X or Y chromosome. It is found on the other 22 chromosomes in the human body. This means that men and women have an equal chance of having the disorder. The mother and father can be homozygous dominant, heterozygous, and homozygous recessive. If a person is homozygous dominant, the person has two of the same dominant genes. For example if someone is homozygous dominant for being tall it may be represented as TT. Capital letter always represent a dominant gene. If a person is heterozygous, this person would have a dominant trait and a recessive trait. It may be represent as Tt. The dominant gene will mask the recessive gene, so the person is still tall. If a person is homozygous recessive, the person has two of the same recessive genes. For example if someone is homozygous recessive for height, it may be represented as tt. The tt would mean the person is short.

11. Example of Pedigree Charts
Is it Autosomal or X-linked?
Take a minute and try to decide if this slide is autosomal or X-linked.

12. Answer
Autosomal
It is autosomal because it is 50/50 men to women with the disorder, if it was X-linked most of the men in the diagram would have the disorder.
Make sure you count the number of men with the disorder and the number of women with the disorder. In this pedigree, 3 men and 3 women have the disorder.

13. Interpreting a Pedigree Chart
Determine whether the disorder is dominant or recessive.
If the disorder is dominant, one of the parents must have the disorder.
If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.
The second step is to determine if the disorder is dominant or recessive. It is important to find out if a disorder is dominant or recessive. For example, Huntington’s disease is a dominant disorder. If you have only one dominant gene you will have Huntington’s disease, which is a lethal disorder. The disorder does not show up until a person is in their middle ages such as 45. It will quickly decrease their motor skills and the brain will begin to deteriorate.
If a disorder is dominant, one parent must have the disorder (either homozygous dominant (TT) or heterozygous recessive (Tt). Both parents do not have to have the disorder. One parent might not have the disorder or be a carrier. If a disease is dominant, it does not skip a generation unless one parent is heterozygous dominant (Tt) and the other parent is homozygous recessive (tt). In this case the child has a chance of not receiving the dominant gene.
If the disorder is recessive, a parent does not have to have the disorder, but could still pass it to their offspring. This would happen when a parent is heterozygous recessive (Tt) and passes on the recessive (t) gene. This means this disorder can skip generations. An example of a recessive disorder would be sickle cell anemia.

14. Example of Pedigree Charts
Dominant or Recessive?
Is this pedigree dominant or recessive?

15. Answer
Dominant
It is dominant because a parent in every generation have the disorder. Remember if a parent in every generation has the disorder, the disorder has not skipped a generation. If the disorder has not skipped a generation the disorder is dominant.

16. Example of Pedigree Charts
Dominant or Recessive?
Is this pedigree dominant or recessive?

17. Answer
Recessive
It is recessive because a parent in every generation does not have the disorder. Remember the disorder can skipped a generation if the disorder is recessive. The parents can be heterozygous and be carriers of the disorder but not have the symptoms of the disorder.

18. Genetic Diseases Autosomal Dominant Achondraplasia
Dwarfism
Huntington’s Disease
brain disorder that affects a person's ability to think, talk, and move.

19. Autosomal Recessive Cystic Fibrosis Lung infections
Mutation stops production of a protein found in the cells of lungs and other organs – leads to thick mucus and bacterial infections of the lungs.

20. Autosomal Recessive PKU Maple Syrup Urine Disease
Smaller than normal head, epilepsy, mental retardation
Mutation in gene that breaks down phenylalanine (an amino acid found in the body and in some foods like proteins and diet drinks)
In the US, babies are screened at birth b/c it can be treated with diet
Maple Syrup Urine Disease
Can’t break down certain amino acids. Build up causes brain damage.
Treated with restricted diet (no protein!)

21. Sex-Linked Recessive Women = XX Men = XY Hemophilia Bleeding disease
Mutation in clotting factor gene
Sex linked disorder
1 in 4,000 males, rare in females
Gene is found on the X chromasome. How does this affect men and women differently?

22. Co-Dominant
Not all genes have dominant and recessive alleles. Some have alleles that are both expressed together in the heterozygote individuals.
Co-dominant alleles have three phenotypes, one for each genotype.
Sickle Cell Disease
Normal -- two normal hemoglobin alleles
Sickle cell trait -- heterozygotes, having one of each allele: a mild condition where 50% of the red blood cells are affected.
Sickle cell anemia -- two sickle cell alleles in their genotype: a severe form where all the red blood cells are affected.

23. Homework In your textbook: Chapter 14 p. 363
Answer # 1, 2, 5, 6, 7, 8, 14, and 15